Thickened butadiene-styrene latices

ABSTRACT

Butadiene-styrene latex thickened with an emulsion containing a terpolymer derived from (1) methacrylic acid or ethacrylic acid; (2) a C 1-8  alkylester of acrylic, methacrylic or ethacrylic acid, and; (3) acrylamide or styrene optionally nuclearly substituted by methyl or ethyl.

This is a division of application Ser. No. 770,197, filed Feb. 18, 1977and now U.S. Pat. No. 4,128,520.

FIELD OF THE INVENTION

This invention relates broadly to emulsion terpolymers prepared from, asmonomers, (1) an α,β-unsaturated carboxylic acid of the formula ##STR1##where R is methyl or ethyl, (2) an ester of an α,β-unsaturatedcarboxylic acid of the formula ##STR2## where R₁ is alkyl of from 1 to 8carbon atoms and R₂ is hydrogen, methyl or ethyl, and (3) an amide of anα,β-unsaturated carboxylic acid of the formula ##STR3## or anunsaturated aromatic hydrocarbon of the formula ##STR4## these are lowviscosity emulsions, useful as thickeners, particularly forbutadiene-styrene base synthetic latices.

A preferred embodiment of this invention relates to terpolymers whereinone of the termonomers is an α,β-unsaturated carboxylic acid amide orstyrene; a second monomer is methacrylic acid, and the third termonomeris ethyl acrylate.

DESCRIPTION OF THE PRIOR ART

Various types of thickeners or thickening agents are known in the art.Some, such as those described in U.S. Pat. No. 3,810,859, describeemulsions which contain a small amount (0.5-6%) of an organic acidtogether with a glycidyl monomer. While such emulsions themselves aresaid to be thickenable, no doubt via cross-linking, it is not,nevertheless, within the contemplation of this patent to utilize suchemulsions to thicken other emulsions.

Other types of thickeners, such as those disclosed in U.S. Pat. No.3,657,175, involve emulsions entailing a complex formula, e.g. such asone derived from monomers of butadiene, styrene, methacrylic acid, andan ethoxylated alcoholic half ester of maleic acid. However, in orderfor such emulsions to be stable, butadiene and styrene have to bepresent, along with the maleic acid half ester, which is itself said tobe an essential ingredient.

U.S Pat. No. 3,035,004 relates broadly to certain copolymers ofmethacrylic acid and alkyl acrylates containing no more than 56% ofmethacrylic acid, but does not relate at all to terpolymers. Moreover,the emulsions of U.S. Pat. No. 3,035,004 are prepared by a method, thatis entirely different from the one disclosed herein. Therefore, theemulsions resulting from such copolymers are chemically different fromthose of the present invention, as exemplified by the differences iskind of each of those in respect of their respective viscosities inwater, when neutralized to pH 7.0. Accordingly, a copolymer emulsionmade by the process of U.S. Pat. No. 3,035,004 with 53/47 methacrylicacid-ethylacrylate monomer ratio, when used at 0.5% concentration,increased the viscosity of water only to 18.5 cps. The result obtainedunder the same conditions with one of the terpolymers of the inventionwas 1568 cps--Example II--that is, eighty-five fold higher. Furthermore,the emulsions of U.S. Pat. No. 3,035,004 are latices of poor stabilityand separate on standing. Therefore, they have to be transformed intowater soluble salts in order to be useful. On the other hand, thelatices of our invention are of very good mechanical andshelf-stability.

SUMMARY OF THE INVENTION

This invention relates generally to thickening agents and particularlyto a method for increasing the vicosity of butadiene-styrene latices byadding thereto an emulsion comprising a terpolymer structure containingthe following repeating units: ##STR5## where each R is methyl or ethyl,R₁ is alkyl of from 1 to 8 carbon atoms, and R₂ is hydrogen, methyl orethyl. The monomers are, respectively (1) an α,β-unsaturated carboxylicacid having from 4 to 5 carbon atoms (2) an alkyl ester and preferably,a lower alkyl ester (C₁ -C₄) of an acid defined by (1), and (3) theamide of an acid defined by (1) or styrene or a styrene derivative ofthe formula ##STR6##

These terpolymer emulsions themselves are of low viscosity but act asthickening agents when added to butadiene-styrene latices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment, the emulsion comprises a terpolymer structurewith repeating units, respectively, of (1) methacrylic acid, (2) methylacrylate or ethyl acrylate, preferably ethyl acrylate, and (3)acrylamide, or styrene or its derivatives such as vinyl toluene,1-vinyl-4-ethylenzene and the like.

In a preferred mode of practice of the present invention, the emulsioncontains monomer units of at least three different kinds in thefollowing amounts and proportions:

(1) from about 30 percent to about 85 percent, preferably from 50percent to 70 percent, by weight of an α,β-monoethylenically unsaturatedcarboxylic acid of Formula I, preferably methacrylic acid, ethacrylicacid or mixtures thereof with other unsaturated carboxylic acids such asacrylic acid. The amount of such other unsaturated carboxylic acidswhich can be employed in such mixtures can vary up to about 50% or moreof such mixtures depending upon the concentration and hydrophobic natureof the carboxylic acid ester units in the resulting polymer. As theconcentration and/or hydrophobic nature of the ester increases,increasing amounts of such other unsaturated carboxylic acids, e.g.,acrylic acid, can be employed to the extent that a stable latex canstill be obtained.

(2) from about 5 percent to about 50 percent, preferably from 20 percentto 30 percent, by weight, of at least one alkyl ester of Formula II,preferably ethyl acrylate;

(3) from about 0.5 percent to about 20 percent, preferably from 3percent to 8 percent, by weight of an amide of Formula III, i.e.,acrylamide, or an unsaturated aromatic hydrocarbon of Formula IV,preferably styrene. The presence of the amide of the unsaturatedaromatic hydrocarbon is an important feature of this invention, since byinclusion of either of these termonomers into the polymer structure, therheology of systems into which such resultant polymer structure isintroduced can be changed drastically, and in an unexpected fashion anddegree.

It is to be understood, however, that all the foregoing percentages arebased on the total copolymer weight, and they have to total 100%.

Beside the aforedescribed termonomer types, small amounts of somebifunctional, ethylenically unsaturated cross-linking monomer may alsobe added to the mixture. This monomer has to be capable of polymerizingunder free radical conditions so as to covalently bond different chainsof the polymer. Polyfunctional monomers, such as divinyl benzene,polyethylene-glycoldimethacrylate, methylene-bis-(acrylamide), etc., areillustrative examples. Other monomers, which can render the polymercurable (through heat-treatments) or otherwise cross-linkable, such asmethylolacrylamide, glycidylmethacrylate, epoxybutadiene, etc., can alsobe used as comonomers.

Chain transfer agents can be used to regulate the average molecularweight of the polymer. Preferred agents are mercaptans such ast-dodecylmercaptan.

The preparation of the terpolymers of this invention is carried out inan emulsion system. The term "emulsion" as used herein, is intended tomean a true colloidal dispersion of the terpolymers in water.

Polymerization is effected in the presence of a catalyst or initiator,preferably one which serves as a thermally activated source of freeradicals. Among such catalysts may be mentioned peracetic acid, hydrogenperoxide, persulfates, perphosphates, perborates, percarbonates, etc.The preferred catalyst is ammonium persulfate, as it provides efficientreaction rates and contains a fugitive cation. The amount of initiatorused is normally about 0.03 to 3.0 percent, by weight, based on theweight of the total monomers and preferably from 0.25 to 0.5 percent.Preferably the initiator is a redox combination of the water solublepersulfate as the oxidizing component and a hydrosulfite, e.g., sodiumhydrosulfite, as the reducing component of the redox combination. Watersoluble bisulfites, metabisulfites or thiosulfates, reducing sugars,formaldehyde sulfoxalate, etc., may be used in lieu of thehydrosulfites. Other typical redox combinations, such as sodium azideand ceric ammonium sulfate, titanium trichloride and hydroxylamine, andthe like, may also be used. Generally useful proportions of theindicated persulfate-hydrosulfite system are 0.01 percent to 1.0 percentfor the oxidizing component and 0.015 to 1.5 percent for the reducingcomponent based on the amount of monomers.

The redox combination can be further activated by the presence ofpolyvalent metal ions at the lower oxidation stage, e.g., ferroussulfate, cuprous sulfate and the like. The preferred amount of thesemetal salts may be between 5 ppm and 100 ppm by weight, based on thetotal amount of the monomers.

The aqueous medium for polymerization contains one or more emulsifiersto help disperse the monomers in the aqueous medium, and to protect theparticles formed. Salts of the higher molecular weight sulfonic acids,e.g., alkyl aryl sodium sulfonate, are eminently suitable for thepurpose, though other surfactants may also be used with good results.

The amount of surfactant employed can be varied considerably, butordinarily from about 0.1 percent to about 10 percent, and moreparticularly from about 0.2 percent to about 1.0 percent, by weight,based on the total weight of the comonomers, will be used. Someadditives such as alcohols and the like can also be used in order tohelp the solubilization of insoluble monomers. The concentration ofthese materials can be varied between 0.1 percent and 2.0 percent byweight, based on the weight of the comonomers. The emulsion can alsocontain a small amount of a protective colloid, such as water solublecellulose derivatives, poly(vinylpyrrolidone), alkali metalpolyacrylates, water soluble alginates, and the like. The amount of sucha colloid used can range, for example, from about 0.1 percent to about 2percent and more particularly from about 0.5 percent to 1 percent.

The terpolymer emulsions employed in the present invention typicallyhave from about 15 percent and preferably from about 20 percent to about50 percent solids content. The average particle size of the emulsion maybe from 500 Angstroms or smaller to about 3000 Angstroms or greater.

The reaction temperature employed depends, in the first place, on thepolymerization catalyst and the monomers used. In general, thepolymerization is carried out at a temperature in the range of from 5°C. to 120° C. When the catalyst is a redox system, the recommendedinitial temperature range is 5° C. to 80° C., advantageously, 15° C. to60° C.

It is advisable to operate with the exclusion of oxygen, for exampleunder a neutral gas such as nitrogen, argon, and the like. Sometimes itmay also be advantageous to run the reaction under elevated or reducedpressure.

The polymerization can be run conveniently by a single stage procedure,whereby all the ingredients are charged to the reactor at the same time.Since the polymerization reaction is exothermic, the initiation thereofcan be evidenced by the increasing temperature resulting from additionof the reactants. When the polymerization has proceeded to the extentthat the consumption of the monomers is practically complete, theterminal point is indicated by the cessation in the rise of thetemperature, followed by a temperature drop. The time period necessaryfor the aforedescribed operation can range from about 10 minutes toabout 2 hours.

The terpolymers of this invention are excellent thickening agents andcan influence the viscosity of a variety of systems in an effective andunique way. Not only can they form viscous systems with water baseddispersions of materials that are insoluble in the medium, but they canalso thicken dilute solutions of organic materials soluble in water, aswell as thicken organic materials that are, in and of themselves,miscible with water. Importantly, moreover, they can thicken wateritself, that is at a pH of 7.0 and higher, a unique property which maybe attributed to the high molecular weight of these polymers. Anotherproperty that may contribute to this phenomenon is the uniquely highacid content of the terpolymers. The viscosity of a solution at pH 7.0which contains a little as 0.5% (total solids basis) of theseterpolymers can be as high as 2000 cps or more as compared to a fewhundred centipoise viscosities obtained by thickeners made underdifferent circumstances. The unique thickening properties of theseterpolymers makes them suitable for a variety of applications.

Only a relatively small amount of the terpolymer latices of the presentinvention are required to produce significant thickening of thebutadiene-styrene latices with which such terpolymers are blended. Suchblends can contain from about 0.1 to about 5% of the terpolymer on atotal solids basis and preferably, from about 0.5 to about 2% of theterpolymer on a total solids basis.

It is known that textiles used in the manufacturing of broadloom carpetsor used as upholstery fabrics can be treated with various materials ofwhich copolymers of butadiene and styrene have previously been found tobe the most suitable. The textile that has been treated with suchcopolymers acquires various excellent properties, for example, built upbody, resiliency, tear resistance, abrasion resistance, pleasing "hand",and retention of textile character. However, when the textile is treatedin such a way that the coating has to be applied only on one side of thesubstance, the viscosity of the coating system has to be increased to anextent such that it does not penetrate through the network formed by thetextile fibers. The terpolymers of the present invention are uniquelysuited to increasing the viscosity of aqueous dispersions ofbutadiene-styrene copolymers. In addition to increasing the viscosity ofsuch dispersions, moreover, it is further demanded that the thickenerimpart a degree of thixotropy, so that the viscosity of the coatingdecreases during the application, but retains its high value again,after the shear of application disappears. In general, without wishingto be bound or limited by any theory, it can be said that theterpolymers of this invention have been found to perform according tothis principle.

It is generally known, for example, that the viscosity of a carboxylicacid polymer can be increased by:

a. solubilization of the polymer through salt formation, or

b. swelling of the polymer by hydration of the ion pair.

From these, it might have been concluded by those skilled in the artthat the viscosity would, of necessity, have to be a function of theconcentration of the carboxylic acid only. However, in the case of thepresent terpolymers, surprisingly, it was nevertheless found that it wasthe presence of the acidamide or aromatic hydrocarbon unit that made theterpolymers of this invention so exceptionally active with thebutadiene-styrene copolymer latices. By way of contrast, systems whichdid not contain the amide or the aromatic hydrocarbon termonomer showedsignificantly decreased activity. It is believed that the compatabilityof the amide of aromatic hydrocarbon unit with the butadiene-styrenesubstrate is responsible for the unique behavior of the terpolymers ofthis invention.

The terpolymers aforedescribed are particularly useful to change therheological behavior to butadiene-styrene base synthetic latices.However, they can be used also for the thickening of the dispersions ofwater insoluble and water soluble polymers of all types. Examples ofwater insoluble dispersions may include natural rubber latices, emulsionpolymers of acrylic and vinyl types, as well as their copolymers.Poly(vinylpyrrolidone), poly(acrylamide), poly(vinyl methyl ether),etc., may serve as examples for the thickenable water soluble species.Another important property of the terpolymers of this invention is thatthey are eminently suitable to increase the viscosity of water itself.That is, to produce high viscosity solutions when dissolved in water,even at very low concentrations.

An important feature of this invention is that its subject polymers canbe prepared as low viscosity emulsions and that they can act as "insitu" thickening agents. By the term "in situ" --as it is usedherein--is meant that a system of high viscosity can be prepared byadding a low viscosity acid emulsion to a low viscosity alkalinesolution or dispersion, and by blending these two ingredients into auniform system. Of course, the latter ingredient can also be neutral oreven slightly acidic in which case, the high viscosity can be achievedby simple adjusting of the pH of the blend above the neutral point. Thisis a distinct advantage over the use of other known thickening agents,such as salts of acrylic acid, cellulose derivatives, natural gums,etc., which have to be stored and used as high viscosity solutions.Because of the high viscosity of such solutions, they are difficult tohandle, and usually demand special equipment to achieve thoroughblending with the substrate. By way of contrast to those thickeners, theemulsions of this invention are of very low viscosity (usually on theorder of less than 50 cps). Therefore, they can be stored and handledwith ease.

While the water soluble polymers and insoluble dispersions that are mostpreferred for purposes of being thickened by the terpolymer emulsionsusable in this invention, are those most conveniently used for the backof upholstery fabrics or carpets, nevertheless such polymers anddispersions can also be used for coating, impregnating, cementing andlaminating textiles as well as for dressing, sizing and finishing ofpaper, leather, felts, and the like. The aqueous solutions anddispersions to be thickened can contain all sorts of other substancesconventionally suitable for enhancing the properties of the thickenedsystem, such as fillers, pigments, stabilizers, curing agents, binders,foaming agents, dyes and other such additives. They are applicable alsoin the thickening of cosmetic preparations such as creams, lotions andhair grooming aids. In addition, however, they can also be used asthickening agents for paints, printing inks, detergents and cleaningcompositions, and the like.

The terpolymers can be made water soluble through the addition of somebase such as sodium hydroxide, ammonium hydroxide and the like. Theanionic polyelectrolytes prepared by this fashion are particularlyuseful thickeners, dye leveling agents, anti-migrants, flocculants,sewage treatment aids, protective colloid agents, drilling mudstabilizers, and in other fields of application.

The following examples are provided to illustrate the principles andpractice of this invention. However, it will be understood that theseexamples are not to be construed as limiting the scope of the presentinvention in any manner.

In these examples all parts and percentages are by weight, unlessotherwise indicated.

EXAMPLE I Method of Testing

A 400 ml. beaker is tared on an electric top-loading balance, and 200grams of carboxylated butadiene-styrene latex (GAF-1400 available fromGAF Corporation, Chattanooga, Tenn.) is weighed in it with 0.05 gramaccuracy. (The solid content of the latex is 50%). After that, thesample to be tested (for which the solid content of the sample had beendetermined previously) is weighed in a 100 ml. beaker, under similarconditions. The amount of the sample is made to give exactly 1.0 grampolymer solids. To this sample, distilled water is added to make thetotal weight of the sample 80.0 grams. The 400 ml. beaker holding thebutadiene-styrene latex is placed under an electric stirring apparatus,equipped with a Teflon-lined, three blade stirrer of 13/4 inch diameter.The beaker rests on a lab jack in such a way that the tip of the stirreris 1 inch above the bottom of the beaker. Agitation is started with 800r.p.m., and the diluted sample is added to the latex within 15 seconds.The agitation is continued for exactly three minutes while moving thebeaker slowly up and down to insure good mixing. After that, the beakeris removed and the viscosity of the thickened latex is determinedimmediately with an LVF Brookfield viscosimeter, using Spindle #4 at 12r.p.m.

This method was found to give a reproducibility of ±100 centipoises orbetter.

EXAMPLE II Preparation of Methacrylic Acid-Ethylacrylate-StyreneTerpolymer

Apparatus:

5 liter resin kettle, equipped with mechanical stirrer, refluxcondenser, thermometer and gas inlet tube.

Procedure:

Under a blanket of nitrogen, the following ingredients of the reactionwere charged, with agitation, in the following order and amounts:

2823.8 g. distilled water,

14.3 g. Siponate DS-10, (25% dodecylbenzene sodium sulfonate, Product ofAlcolac Co.)

10.7 g. n-butanol,

472.0 g. methacrylic acid,

200.1 g. ethylacrylate,

42.9 g. styrene,

0.023 g. divinylbenzene (60%)

2.85 g. of a 10% ammonium persulfate solution and

4.77 g. of a 0.1% ferrous sulfate solution.

At this point, the agitation was stopped, and 3.57 g. of a 10% solutionof concentrated sodium hydrosulfite (Lykopon available from Rohm & HaasCo.) was introduced. Five minutes later, slow agitation was started, asa slight temperature rise (from 22° C. to 23° C.) signalled that thereaction had already begun. Five minutes later, at 26° C., the speed ofthe agitation was adjusted to 150 RPM. After that, the temperature rosesteadily and peaked in 20 minutes at 52° C. After that, the system wasallowed to cool to room temperature, and the product--a free flowingmilky latex--was discharged through a 100 mesh screen.

The following examples IV-X are comparative.

EXAMPLE III

Emulsion terpolymer is prepared by the process described in Example II,except that the termonomer is acrylamide. Ratio of methacrylicacid-ethylacrylate-acrylamide: 66/28/6.

EXAMPLE IV

Emulsion copolymer is prepared by the process described in Example II,except that the emulsion is made without termonomer.

Ratio of methacrylic acid-ethylacrylate 70/30.

EXAMPLE V

Emulsion copolymer is prepared by the process described in Example II,except that the comonomer is methylacrylate instead of ethylacrylate,and the system does not contain termonomer.

Ratio of methacrylic acid-methylacrylate 60/40.

EXAMPLE VI

Emulsion terpolymer is prepared by the process described in Example II,except that the termonomer is vinylacetate.

Ratio of methacrylic acid-ethylacrylate-vinylacetate: 66/28/6.

EXAMPLE VII

Emulsion terpolymer is prepared by the process described in Example II,except that the termonomer is vinylpyrrolidone.

Ratio of methacrylic acid-ethylacrylate-vinylpyrrolidone: 66/28/6.

EXAMPLE VIII

Emulsion terpolymer is prepared by the process described in Example II,except that the termonomer is diethylmaleate.

The ratio of methacrylic acid-ethylacrylate-diethylmaleate: 66/28/6.

EXAMPLE IX

Emulsion terpolymer is prepared by the process described in Example II,except that the termonomer is halfacid ethylmaleate.

Ratio of methacrylic acid-ethylacrylate-termonomer: 66/28/6.

EXAMPLE X

Emulsion terpolymer is prepared by the process described in Example II,except that the termonomer is triethoxy vinyl silane.

Ratio of methacrylic acid-ethylacrylate-termonomer: 66/28/6.

    __________________________________________________________________________    SUMMARY OF THE RESULTS                                                        The emulsions of Examples II-III and Comparative Examples IV-X were           compared as to their thickening                                               effect on butadiene-styrene latices. The procedure of Example I was           repeated, using r.p.m. of 6,12, 30 and 60. The                                results are summarized in the following table which shows Brookfield          viscosities in cps:                                                                       Example                                                                       INVENTION                                                                              COMPARATIVE EXAMPLES                                                                                         X                                          III         VI  VII    VIII IX     Triethoxy                             II   Acryl-                                                                            IV  V   Vinyl-                                                                            Vinyl- Diethyl                                                                            Half-Acid                                                                            Vinyl-                    Termonomer  Styrene                                                                            amide                                                                             None                                                                              None                                                                              acetate                                                                           Pyrrolidone                                                                          Maleate                                                                            Ethylmaleate                                                                         Silane                    __________________________________________________________________________    Brookfield Viscosity                                                                     6                                                                              37,000                                                                             23,300                                                                            9,700                                                                             6,500                                                                             5,720                                                                             13,500 12,200                                                                             10,000 5,800                     cps. on LVF Sp #4                                                                       12                                                                              18,600                                                                             14,000                                                                            5,500                                                                             3,750                                                                             3,430                                                                             6,950  6,800                                                                              5,800  3,600                     RPM       30                                                                               9,150                                                                              7,000                                                                            2,600                                                                             1,900                                                                             1,800                                                                             3,520  3,360                                                                              3,010  2,900                               60                                                                               5,170                                                                              4,150                                                                            1,500                                                                             1,170                                                                             1,120                                                                             2,010  2,050                                                                              1,880  1,650                     __________________________________________________________________________     In Examples II, III and Comparative Examples VI-X, the weight ratio of        methacrylic acid/ethyl acrylate/termonomer was 66/28/6. In Comparative        Example IV, the weight ratio of methacrylic acid/ethyl acrylate was 70/30     In Comparative Example V, the weight ratio of methacrylic acid/methyl         acrylate was 60/40.                                                      

What is claimed is:
 1. A butadiene-styrene latex containing an effectivethickening amount of a terpolymer emulsion prepared by inducing in areactor, at a temperature of about 5° C. to about 80° C., aredox-initiated polymerization in an aqueous dispersion of, as monomers,(1) about 30 to about 85 wt% of methacrylic acid (2) about 5 to about50% wt of ethyl acrylate, and; (3) about 0.5 to about 20 wt% ofacrylamide, all the ingredients necessary for said polymerization beingpresent in said reactor upon initiation of the polymerization.
 2. Alatex according to claim 1 in which the range of monomer (1) is from 50to 70 wt%, the range of monomer (2) is from 20 to 30 wt.%, and the rangeof monomer (3) is from 3 to 8 wt%.